1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing lost wax molds for making cast parts manufactured with a lost wax process and to cast parts made from the molds resulting from such a manufacturing method, and particularly to a lost wax mold manufacturing method which allows each process of lost wax mold manufacturing to be unmanned, automatic and continuous.
2. Description of the Background Art
The cost of manufacturing metallic parts and the like having many parts or complicated shape that need to be machined can be sharply reduced by changing the manufacturing method to a die casting or casting using a lost wax. While die casting is limited to the metal materials of aluminum or its alloy, lost wax is applicable to a variety of metallic parts made of such materials as iron and copper.
As is already known, a wax tree 1 is made by joining one or more wax product-patterns 2 and a gate stick 3 as shown in FIG. 15. The mold made from a lost wax process is used for manufacturing metallic parts, as indicated in FIG. 14a. Initially, the wax tree is assembled and degreased (steps S11 and S12). Subsequently, in a series of successive coating and drying steps (S13-S26) the wax tree is put into a slurry dipping bath filled with a slurry fluid to coat the wax tree evenly with the slurry fluid to prevent bubbles from sticking thereto, is rid of the fluid, and is then coated with sand in a sanding fluidized bed tank and dried. These steps are repeated to provide the wax tree with several coats of sand until the wax tree is thick enough to endure pouring pressure. The combination of assembled wax patterns which are coated with sand are generically referred to as the wax tree (or the tree). Then, in step S27, the sand-coated wax tree is heated to fuse and run off the wax (dewax), and the remaining sand mold is calcined (step S28). Subsequently, molten metal is poured through the sprue of the sand mold, the sand mold is cooled and broken to separate a desired metallic part therefrom for use as a product or a product part (steps S29-S31).
Among the several coats of sand thus applied, the first coat that relates to the casting surface of the part uses fine sand in order to assure a good surface finish. Since bubble build-up between the wax tree and the slurry fluid in the first coating deteriorates the casting surface, a worker checks for bubbles and removes them, if any, with a spoon tool or the like. The third to the sixth coating processes, which are identical in procedure to but are different in sand roughness from the first coating, comprise dipping, fluid ridding, sanding and sand stripping (steps S111-S114), as indicated in FIG. 14b. Unlike the first and the third to the sixth coating processes, the second coating process pre-dips the wax tree (step S110) to prevent bubbles from occurring between the first coat of sand and the slurry fluid before it is dipped in the slurry fluid as indicated in FIG. 14c. The seventh coating process, which includes only dipping into the slurry fluid and fluid ridding as indicated in FIG. 14d, is conducted to ensure that the sixth coat of sand is applied to the wax tree more reliably.
In the above lost wax mold manufacturing process, wax trees produced on a small to medium scale were coated manually in most cases, and if a partially mechanized method is employed, coating was supplemented by manual work.
FIG. 16 is a plan view of an automatic coating apparatus presented in Japanese Laid-Open Patent Publication No. SHO55-86657, wherein the numeral 101 indicates wax trees and 102 designates wax tree carts which transport the wax trees 101. 103 denotes a wax tree removing device, 104 represents a slurry dipping device, 105 indicates an excess slurry centrifuging device, 106 denotes a sanding device, and 108 represents a wax tree transfer device. These devices are arranged at equal intervals on a circumference with a wax tree feeding device 109 at the center. A spare slurry tank 110 and a spare sand tank 111 are disposed at the back of the slurry dipping device 104 and the sanding device 106, respectively. The wax tree carts 102 are set on rotary tables 112. 113 designates a control panel which controls all functions to handle all these components as an integrated system.
FIG. 17a is a partial plan view of the wax tree feeding device 109 and FIG. 17b is a partial front view thereof, wherein 109a indicates a hydraulic cylinder for moving a vertical spindle 109b up and down. At the top of the spindle 109b, there are six beams 109f extending at intervals of 60.degree. perpendicularly to the spindle on a level with each other. The beams 109 are swung 60.degree. by a rotary cylinder 109d. At the end of each beam 109f, an arm seat 109h is movable by a hydraulic cylinder 109g in the longitudinal direction of the beam along a slide shaft 109i and the arm seat 109h is fitted with arms 109j. When the spindle 109b comes down, these arms 109j lower, then retract inwardly to fit the wax tree 101 to the corresponding device. The spindle 109b rises again, rotates 60.degree. in the opposite direction and lowers, and the arms 109j are then pushed outwardly to return to the original position. Between the slurry dipping device 104 and the excess slurry centrifuging device 105 and between the excess slurry centrifuging device 105 and the sanding device 106, motors (not shown) fitted to the arm seats 109h are used to rotate the wax trees to remove excess slurry, to prevent the slurry from uneven distribution, and to prevent excess sand from being scattered. Also, when treatment work in any of the devices is finished earlier than in the others, its wax tree is made ready to be removed and that device waits for the other devices to complete their works. If the device waiting is, for example, the slurry dipping device, it holds the wax tree to keep the tree away from the slurry fluid while waiting and simultaneously rotates the wax tree by means of a motor 104e to prevent the uneven distribution of the slurry as shown in FIG. 18. As described above, this automatic coating apparatus allows the coating work to be done by one worker, and if the adjustment and supply of materials are completed before operation, the worker only needs to perform a monitoring activity and is not required to perform heavy labor under a monotonous, hostile environment, whereby safety is ensured and production efficiency can be improved greatly.
In the conventional lost wax mold manufacturing apparatus designed as described above, the quantity and time allowed for consecutive automatic operation are limited by the shape and system of the carts which store the wax trees and the whole apparatus must be stopped to supply the materials such as the slurry and sand. Also, each device must be arranged at equal intervals on a circumference and the work time of the whole apparatus must be set to that of the device requiring the longest time. Further, the management of drying time after the formation of each coat, which is an important factor in retaining quality in the lost wax mold manufacturing, is not referred to for this apparatus. Furthermore, the ways of troubleshooting faults, such as wax tree breakage, are not described for this apparatus and fully unmanned operation cannot be performed, requiring the worker to continuously monitor the operation.